SARS-CoV-2 seroprevalence among workers after a COVID-19 outbreak in POYUN company, Hai Duong province, Vietnam, 2021

In late January 2021, there was a community outbreak of SARS-CoV-2 at Poyun Electronics Ltd. company in Chi Linh City, Hai Duong province, Vietnam. In response, the national vaccination program was implemented for the entire Vietnamese population. To better understand the correlation between people who were infected with SARS CoV-2 and those who received the vaccine, we conducted a serology study on Poyun company workers seven months later the COVID-19 outbreak in March 2021. Our study involved collecting serum samples and conducting ELISA tests to detect antibodies against the S and N proteins of SARS-CoV-2. We also collected information on infection and vaccination through a questionnaire. The study included 881 participants, in that 184 were COVID-19 patients and 697 were not. Of the participants, 806 had received one/two shots of the COVID-19 vaccine, of whom 60.7% had receivedthe BBIBP-CorV the antibody against SARS-CoV-2 infection. Among non-infected Poyun company workers, more than ninety percent had SARS-CoV-2 antibodies three weeks after 1 or 2 shots of vaccination. This study is the first report to provide initial information about antibody development against SARS-CoV-2 induced by natural infection and COVID-19 vaccination in the Vietnamese community.